This invention relates to semiconductor pressure transducers and, more particularly, to such transducers which are formed to compensate for signals occurring at zero pressure differential.
The semiconductor pressure transducers known in the prior art employ a diaphragm responsive to the pressure differential across the two surfaces thereof. The transducer is formed of a single crystal semiconductor chip. A circular cavity is formed in one surface of the chip, and a cylindrical glass tube for communicating the pressure to be measured has one end thereof bonded to such one surface of the chip to surround the cavity. The diaphragm comprises the portion of the chip overlying the cavity. Stress sensors are disposed on the other surface of the chip above the cavity. Stress sensors which are widely used for this purpose exhibit a piezoresistive characteristic, whereby the resistance of the sensor varies with the stress experienced by the sensor as the stress in the chip changes with the differential pressure.
Normally at least one pair of radial stress sensors and one pair of circumferential stress sensors are disposed on the diaphragm. These sensors are electrically connected together, such as in a bridge circuit, to provide signals representing the differential pressure on the diaphragm.
Semiconductor pressure transducers of the type described generate false or spurious signals, termed "zero shift", as the static pressure (i.e., common to both surfaces of the diaphragm) or the temperature of the transducer varies. Specifically "zero shift" means a signal that changes as a result of some influence that occurs at zero pressure differential across the transducer diaphragm. Because of this zero shift phenomenon the semiconductor pressure transducer of the prior art requires some form of electronic signal compensation in order to be employed reliably for the measurement of differential pressures.
Prior art semiconductor pressure transducers have employed separate pressure sensors and separate temperature sensors to generate separate signals to separately compensate for the two sources of zero shift. However, it would be desirable to provide a single type of device capable of providing a single signal capable of compensating for both sources of zero shift.
Accordingly, it is the principal object of the instant invention to provide an improved semiconductor pressure transducer.
Another object of the instant invention is to provide a semiconductor pressure transducer provided with means for compensating for the zero shift characteristic.
Another object of the instant invention is to provide a semiconductor pressure transducer provided with a single type means for compensating for spurious signals caused by both static pressure changes and temperature variations.